In the presently manufactured portable electronic device in which a main body portion and a liquid crystal portion can be folded, a hinge function is actuated and an opening-closing operation is performed automatically when the liquid crystal portion is opened to a predetermined angle from a closed state.
In particular, the hinge for a cellular phone is configured such that when a telephone conversation, mail, or camera function is realized from a state in which the liquid crystal portion is closed, the liquid crystal portion is opened by inserting a finger into a gap between the main body portion and the liquid crystal portion or pinching and lifting the liquid crystal portion with a hand. In presently manufactured typical products, after the liquid crystal portion is opened from a rotation start (central angle 0°) to a central angle of 70° to 90°, the hinge function is actuated and the liquid crystal portion is automatically opened. In the presently manufactured typical products, the maximum opening angle is set close to a central angle of 165°.
Further, in most products, where the liquid crystal portion is tilted from the completely opened position in the closing direction and the hinge is rotated when the liquid crystal portion is closed, the liquid crystal portion is automatically closed from a vicinity of about 70° to 60°.
Thus, in the presently used single-shaft hinge, a hinge shaft is passed through a first cam and a second cam (usually called “sliding cam”) having formed therein large sliding slanted surfaces on the left and right sides with respect to a protrusion apex as a center in such a configuration that the sliding surface of the second cam faces a protrusion of the first cam, the second cam is impelled by the repulsion force of a compression coil spring, and a rotational sliding torque is generated between the first cam and the second cam.
In most presently used single-shaft hinges, a 180-degree symmetrical cam is used in which concave-convex surfaces are formed in four locations for every 90° in the circumferential 360° direction of the sliding cam in order to realize a variety of functions such as a 360° rotation and clockwise-counterclockwise rotation of the hinge.
This is a mechanism in which, at the abutment surface of the sliding cam, apexes and concave-convex surfaces such as slanted surfaces are formed symmetrically and precisely at 180°. In such a mechanism, the rotation torque caused by friction of abutment surfaces of the cams changes depending on the spring force and position of the concave-convex surface for every 90°.
As for the opening-closing angle of the liquid crystal portion and the arrangement of concaves and convexes on the sliding cam, a minimum torque value is attained when abutment is realized in the concave portion of the sliding cam in the arrangement of concave-convex surfaces. Therefore, this position is designed at a central angle of 0° (fully closed state) or 180° (fully open state).
Further, since the torque value is usually at maximum in the apex of the convex portion reached by rotation through 90°, the vicinity of this position is taken as an operation initiation portion when the liquid crystal portion is automatically opened and closed.
Configurations described in Patent Documents 1 to 4 are disclosed as portable electronic devices using such a hinge. A configuration described in Patent Document 5 in which a friction function is added to the hinge function to change the torque characteristic and a configuration described in Patent Document 6 in which the rotation angle is limited to a maximum of 180° by adding a rotational angle restricting mechanism have been suggested as configurations additionally including special characteristics.